Mutation assays of ethyl methanesulphonate, benzidine and benzo[a]pyrene using Chinese hamster V79 cells

As a contribution to the third UKEMS collaborative trial, ethyl methanesulphonate (EMS), benzo[a]pyrene (B[a]P) and benzidine (BZD) were examined for mutagenicity at the hprt locus in Chinese hamster V79 cells, as assessed by 6-thioguanine (6TG) resistance. EMS was examined in the absence of any exogenous metabolic activation system, and the mutagenic dose-response obtained served to calibrate the assay. B[a]P and BZD were examined using three levels of Aroclor 1254-induced rat liver S9 supplemented with standardized concentrations of cofactors for NADPH generation. B[a]P showed S9 mediated cytotoxicity and mutagenicity, with the magnitude of both responses decreasing with increasing amounts of S9. No evidence of mutagenicity was seen for BZD with any of the metabolic activation conditions employed.